1. Field of the Invention
The invention concerns a threaded tubular connection comprising a male tubular element comprising a male threading (thread profile) and a female tubular element comprising a female threading which can cooperate with the male threading on makeup, said male tubular element having a first annular axial abutment surface and a first annular sealing surface disposed on the radially outer surface of said male tubular element, said female tubular element having a second annular axial abutment surface and a second annular sealing surface disposed on the radially inner surface of said female tubular element, the first and second axial abutment surfaces coming into mutual abutment at the end of makeup while the first and second sealing surfaces come into sealing contact by radial interference, one of the first and second axial abutment surfaces, termed the distal abutment surface, being formed at the free end of a first of said tubular elements, which first element has a lip which extends axially between its threading and the distal abutment surface, and one of the first and second sealing surfaces termed the on-lip sealing surface being disposed on the lip at a non zero axial distance from the distal abutment surface.
That type of threaded tubular connection is intended for the production of strings of tubes for hydrocarbon wells or the like.
2. Description of Related Art
It has been established that in such a threaded connection, when the axial abutment surfaces are axially distanced from sealing surfaces and have a tapered form, termed inverted or with a negative apex angle, such that when they come into mutual abutment, they tend to stress the lip radially towards the surface facing the second tubular element, this in certain cases results in an increase in the contact pressure between the sealing surfaces, improving the seal of the connection against liquids and gases, while in other cases said improvement does not occur or the contact pressure may even be degraded.
Studies carried out to explain this phenomenon have shown that, for a given angle of inclination of the axial abutment surfaces, the behaviour of the lip depends on its radial thickness between the axial abutment surface and the sealing surface. If that thickness is relatively high, the stiffness of the lip is sufficient for the radial thrust exerted by the second axial abutment surface on the first axial abutment surface to be transmitted to the first sealing surface. If, in contrast, the thickness is lower, the lip is not sufficiently stiff and bends, possibly irreversibly, without transmitting the thrust to the sealing surface.
The thicknesses of the lips on the tubular elements may differ for the same nominal diameter. Further, depending on requirements, male elements having different lip thicknesses may be associated with the same female element and conversely. Thus, the problem is to define a common profile for the axial abutment surfaces which can optimize the contact between the sealing surfaces whatever the thicknesses of the male and female lip.
The invention aims to solve this problem.
European patent EP 0 488 912 describes axial abutment surfaces adjacent to the sealing surfaces.
U.S. Pat. No. 3,870,351 describes inwardly curved axial abutment surfaces the inclination of which with respect to the axis changes direction in the radial direction so that their mutual abutment can precisely position the end of the lip but applies no radial force to the whole periphery of the lip.
U.S. Pat. No. 4,611,838 describes axial abutment surfaces extending in a plane perpendicular to the axis of the connection or having a toothed profile such that they lock mutually.
International patent WO 03/048623 describes axial abutment surfaces extending in a plane perpendicular to the axis of the connection or having a constant inclination with respect to thereto, and an on-lip sealing surface axially distant from the axial abutment surfaces.
WO 2004/109173 is equivalent to the foregoing.